Compact lasers that emit radiations in green spectral range with wavelength from 510 nanometers (nm) to 570 nm find their application in various fields ranging from biology and medicine to optical communications and multimedia laser projectors such as picoprojectors.
There exist different techniques to fabricate a compact green laser using different types of laser diodes. One such technique comprises a Diode Pumped Solid State Laser (DPSSL) with Second Harmonic Generation. DPSSL utilizes two-stage light conversion, wherein the first stage includes transformation of laser diode pumping emission into a solid state laser infrared emission and the second stage includes conversion of the solid state laser emission into a second harmonic radiation. The second harmonic radiation emitters have relatively large dimensions, complex design increasing the cost and are not highly efficient.
Another such technique utilizes Second Harmonic Generation (SHG) of laser diodes emission. Laser diodes with SHG use one stage of conversion, wherein an infrared laser diode emission is directly converted to a second harmonic radiation. This ensures small dimensions and high efficiency (Wall Plug Efficiency (WPE)) which is about 10%. SHG lasers make use of periodically poled LiNbO3 crystal for efficient conversion. Since, a crystal of periodically poled LiNbO3 is very expensive, therefore producing cheap laser diodes with SHG on a mass scale is a challenging task.
Direct emitting laser diodes based on InGaN have demonstrated efficient laser emission in green range, however for the green laser emission with a wavelength longer than 540 nm the efficiency of direct emitting InGaN laser diodes drops significantly.
There is a lot of research still going on for efficiently generating compact green laser radiation sources with optimum power value and wavelength.
There is therefore a need of a laser converter that efficiently converts a shorter wavelength laser diode emission (violet-blue) to a longer wavelength green laser emission with a single stage conversion.
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